The control arrangement of a communication system is the intelligence that acts, generally in response to stimuli such as subscriber requests, to determine the configuration of system resources that is necessary to provide subscribers with desired communication services.
Control arrangements are typically designed to provide a predefined set of communication services within a predefined hardware system. This has the unfortunate consequence that addition of new features to the service capabilities of the control arrangements, or porting of the arrangement from one type of system hardware architecture to another, typically necessitate significant changes to, and often a radical redesign of, the whole control arrangement. For example, the traditional design of control software of a telephone electronic switching system typically requires that major modifications be made to the code of both high level functions (e.g., the call processing subsystem, which determines what to do) and low level functions (e.g., the resource management subsystem, which determines how to do it) either when the control software is being ported from one kind of telephone switching system architecture to another, or when new system fabrics and associated features are being added to the software. This, of course, limits the usefulness, cost effectiveness, and portability of the control software.
The above-described characteristics are disadvantageous to control apparatuses of conventional communication systems; they become even more so to control apparatuses of integrated services digital networks (ISDNs). Such networks seek to provide subscribers with many types of voice, data and, in some instances, video, communication services in integrated form, i.e., via a common network and a common interface to the subscribers. These networks tend to be very complex, and their control apparatuses reflect this complexity. Hence, introduction of modifications to the control apparatuses is itself a complex, difficult, time-consuming, and expensive task. Yet the evolution of ISDN technology is young and their architectures are often changing. Also, the services and service features sought to be provided by the ISDNs are progressively expanding. These changes almost invariably require that modifications be made to the network control arrangements to accommodate these changes. But the traditional design of control arrangements typically fails to localize the necessary modifications, and rather makes their extent pervasive. For example, system hardware architecture changes typically require modifications not only to the resource management portion of the control arrangement which manipulates system hardware in order to provide needed communication connections, but also the call processing portion which determines what connections need to be made. Similarly, subscriber feature additions typically require modifications not only of the callprocessing portion, but of the resource management portion as well. But to have to redesign both of these functional portions of network control with each change in network hardware architecture or subscriber features is overly burdensome.
These considerations have led the art to seek to partition control software arrangements into call processing and resource management subsystems in a manner wherein the call processing subsystem operates on a logical abstraction of the physical communication system (also referred to as a virtual machine), and wherein the resource management subsystem translates and maps control functions requested by call processing for the virtual machine into control functions for the actual physical system. The call processing subsystem has thus been made largely independent of various physical implementations of the communication system, the difference being hidden therefrom by the resource management subsystem. As a result, changes in the system physical implementation have come to require changes in the resource management software, but generally not in the call processing software.
A consequence of this approach is that each different physical system implementation generally has a resource management subsystem associated therewith that is different from the resource management subsystems of other physical implementations. This may pose no difficulty in conventional communication systems that provide all communication services via a common communication fabric, such as telephony electronic switching systems that provide both voice and data communications through the same communication switching fabric over the same communication channels. However, certain communication systems that seek to provide integrated voice, data, and video services provide voice and low-speed data services via one communication fabric and provide video and highspeed data services via a completely separate communication fabric.
Such systems essentially comprise two different parallel physical fabrics, and the art's above-described approach to control arrangement design suggests a separate resource management subsystem for each of these fabrics. This approach has the unfortunate consequence, however, that the call processing systems must be made aware of the existence of the two fabrics, and must determine for each call the fabric that will provide or is providing that call so that call processing control function requests for that call may be sent to the appropriate fabric's resource management subsystem. As a result, the call processing subsystem is no longer independent of the system physical configuration, but must be made aware thereof at least to the extent of knowing how many fabrics there are, what the differences between them are, and what the service requirements of each call type are, so that call processing may determine which fabric is appropriate for each call. The desirable quality of call processing's portability across many different system structures and across an expandable variety of services--which quality depends upon the independence of the call processing subsystem from the physical communication system--is, to a degree, destroyed.